CZ154089A3 - stabilized polypropylene and propylene copolymers - Google Patents

Description

The invention relates to polypropylene and its copolymers with ethylene for the production of thin-walled profiles, in particular films, oriented strips and fibers.

In the processing of polypropylene, the material is subjected to a short-term but intense thermal exposure and mechanical stress of the melt in the processing machine. Due to atmospheric oxygen and trace amounts of metals, which are always present in the polymer as residues of the catalyst system, thermo-oxidative degradation of the polymer matrix occurs. If the material is not suitably stabilized, the extent of degradation can be so great that it will prevent its further use.

The polymer is exposed twice to the processing conditions: during the primary processing of the powder into the granulate already in the production plant and then during the actual obtaining of the product from the granulate - in our case, for example, blowing and orienting the foil ev. by passing the melt through a nozzle.

In most cases, the processor recycles the process waste so that part of the material is subjected to three or more treatments.

At present, mainly phenolic antioxidants or their combinations with trivalent phosphorus compounds (phosphites and phosphonites) (GB 1526 603, CS 190 837, EP 184 19D) are used to protect polypropylene from the above degradation effects during processing.

The production of polypropylene fibers and films is one of the most demanding in terms of processing this plastic.

Current stabilization formulas used for this purpose show some drawbacks that cause manufacturing complications. These are mainly the following phenomena:

a) Occurrence of so-called gray granules, the frequency of which is related to the concentration and volatility of the phenolic component. In this case, some granules are contaminated with carbonaceous residues, which cause problems with the blowing and orientation of the film, as the material often breaks up at the point of inhomogeneity.

(b) Yellowish coloring of the natural granulates attributed to the metal-catalysed oxidation of the phenolic component to color products during processing.

For these reasons, there is an effort to reduce the phenolic component content of the stabilizing formula and to utilize the energetic effect that phenolic stabilizers exhibit in combination with phosphites and phosphonites. However, the use of some phosphorous-containing stabilizers may cause other adverse events, such as:

c) Deposit formation in the processing machine.

These deposits clog the filter screen and complicate other manufacturing processes. Deposit analyzes have shown that they are products of the interaction of metal catalyst residues and calcium stearate with products of hydrolysis of organic phosphite.

The following disadvantages are eliminated with polypropylene stabilized according to the invention:

The invention relates to stabilized polypropylene and propylene copolymers with 0.1 to 20% by weight of ethylene containing 0.01 to 1% by weight of phenolic stabilizers and 0.01 to 1% by weight of a mixture of phosphite stabilizers based on the polymer matrix, and optionally further processing additives, in which the phosphite stabilizer mixture is comprised of 10 to 90% by weight of phosphite which is difficult to hydrolyze and 10 to 90% by weight of phosphite is readily hydrolyzable.

By a poorly hydrolyzable phosphite in the definition of the invention is meant a phosphite which after 60 days of storage in a Petri dish (59 mm diameter at 1 g weighing in an atmosphere of 10 ° RH, at 25 ° C, exhibits no more than 7% hydrolysis based on the original component by HPLC) Easily hydrolyzable phosphites were used under these conditions

- 3 hydrolyzes to a higher degree. A typical poorly hydrolyzable phosphite is, for example, tris (2,4-di-tert-butylphenyl) phosphite, while bis (2,4-di-tert-butylphenyl) pentafluoride diphosphite is readily hydrolyzable.

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The invention is based on the use of specific features of the mechanism of action of two types of phosphites. It is known (DG Fobedimskij et al .: Dev. Polym. Stah. 2, 125 (1980)) that phosphitic antioxidants act multifunctionally, primarily through the following chemical reactions: non-radical decomposition of hydroperoxides, reaction with peroxy alkoxy radicals, binding of metal traces and oxidation products of phenolic antioxidants. In particular, the latter two functions are of great importance in preventing the formation of undesirable discoloration of the polymer. An extraordinary bleaching effect is observed in the easily hydrolyzable bis (2,4-di-tert-butylphenyl) pentaerythers and rice pyrophosphites, which during hydrolysis progressively hydrolyzes to the corresponding phosphonate and finally to the corresponding phenol, pentaephthritol and phosphonic acid,

O · - '' - '

This product is a very effective synergistic system of stabilizers (Schwetlick, K. et al., Polym. Leg. Stab. 22,357 (1988)).

It is especially phosphoric acids and their acid esters that effectively bind trace metals.

The mildly acidic environment prevents the oxidation of phenol to the colored quinoid products. The effect of hydrolytic products on the coloring of the polymer is therefore very positive. At higher concentrations, however, they may be the cause of the aforementioned deposits. Phosphite antioxidants that do not readily hydrolyze (e.g. tris - (2,4-di-t-butylphenyl) phosphite) are also effective processing stabilizers, but do not contribute significantly to color improvement. On the other hand, they do not form deposits, as was the case with the hydrolyzable phosphites.

In the invention, the specific properties of the various SK phosphites are used in combination that the hydrolyzable phosphite is only used in an amount necessary to bleach the polymer. High process stability is then achieved by the use of poorly hydrolyzable phosphites. The ratio of the two types of phosphites is chosen according to the processing properties and the degree of hydrolyzability of the easily hydrolyzable phosphites /

Used shortcuts:

PP - polypropylene

A1 - 2,6-di-t-butyl-4-methylphenol

A2 - tetrakis (methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propoxate) methane

A3 - A mixture of 2,6-di-ethyl-4-oligopropenylphenol with a number degree of oligomerization of 15 with unreacted alkylating agent, wherein the content of active substance expressed as the concentration of bound 2,6-dimethylphenol is ,3%.

P-tris £ 4 (1'-phenyl) ethylphenyl-phosphite

P2-bis [(2,4-di-t-butylphenyl) pentaerythritol] diphosphite

P3 - tris [2,4-di-t-butylphenyl] phosphite

P4 - Bis [2-tert-butyl 1-4 - (N, O-dimethylbenzyl) phenyl] pentaentriol diphosphite

P5 - biphenyl) τ4,4 ´ ..- diylbis- ,. tetrakis (2,4-di-t-butyl).

phenyl) phosphonic acid ester

- 5 Table 1

Evaluation of phosphite hydrolyzability f osfit % hydrolysis definition ^F 1 78 easily hydrolyzable ^f 2 98 easily hydrolyzable ^P 3 3 readily hydrolysable ^? 4 91 easily hydrolysable ^F 5 5 readily hydrolysable

hydrolysis measured after 60 days at lab. temperature at 100% relative humidity (phosphite charge 1g)

Example 1

Polypropylene granules prepared from a powdered isotactic Mosten® homopolymer index of 1.5 g / 10 min, with a stabilizer system composition of 0.25, 0.02% A2. 0.08% CaST on the Japan Steel granulation line was subjected to laboratory processing stability measurements, i.e., five times through the Brabender extruder. After each extrusion, the flow index at 230 ° C was measured according to ČSN 64 0861

Furthermore, the yellowness of the original granulate was measured, the A to D of which was determined by a comparative test with a control standard (where A is the lowest yellowness, D the lowest).

Also monitored for the appearance of so-called. _TJ gray granules were counted granules with significantly discolored in randomly collected 500 g of granulate from the granulating lines.

The results are shown in Table 2. Their values show that the stabilization system used in Example 1 is sufficient to maintain processing stability, but does not fully satisfy the requirements in terms of yellowness or gray granules.

Example 2

The PP granulate with the stabilization system composition 0.02% A2 0.08% P2 and 0.08% CaST was prepared in operation and laboratory tested as in Example 1. The results are shown in Table 2. The measured values show that the stabilization system is it not suitable for processing stability, but does it meet the yellow and gray granules requirements?

Example 3

The PP granulate containing the 0.08% P2 and 0.08% CaST stabilizer system was operationally prepared and tested as in Example 1. From the results shown in Table 2, it can be seen that although the degree of yellowness achieved was excellent and the gray granules were not stabilization system is completely unsuitable from the point of view of processing stability.

Example 4

PP granules with a composition of 0.1% A1 0.8% P3 and 0.08% CaST were prepared and laboratory tested in the same manner as in Example 1. From the results shown in Table 2 it is apparent that despite the minimal occurrence of gray granules the degree of yellowness insufficient and processing stability at the usability limit. Flow index values do not guarantee reliability in the event of technological variations in production.

Example 5

PP granulate with stabilizer composition 0.1% A1 θ, 2 2% P2,

0.66% P3 and 68.6% CaST were produced and laboratory tested as in Example 1.

The values in Table 2 show that the stabilization system used provides a very good processing stability, causes minimal yellowness and the presence of gray granules was not detected in the process sample at all.

Example 6

PP granulate stabilized by 0.1% A1, 0.04% P2 system

0.04% P3 and 0.08% CaST were produced and laboratory tested as in Example 1. The values shown in Table 2 show that the stabilization system used is capable of providing all three properties of interest.

Example 7

Granulate P? stabilized with a 0.08% Al, 0.06% P3 and 0.02% P4 and 0.08% CaST stabilization system was prepared and tested in the laboratory in the same manner as in Example 1. The measurement results are shown in Table 2.

Based on these, the system used provides excellent processing stability, high whiteness and suppresses the formation of gray granules. These excellent results as well as the measurement results in Examples 5 and 6 demonstrate a high degree of synergy when using a phenolic stabilizer with a combination of easily hydrolyzable and poorly hydrolyzable phosphite.

Example 8 ·

PP granules stabilized with 0.1% A1, 0.1% A3 0.1% P1 and 0.08% CaST were prepared and laboratory tested as in Example 1. The measurement results are shown in Table 2.

In terms of processing stability, the system proved to be sufficient. In terms of yellowness, however, it is on the acceptability limit and the observed occurrence of gray granules indicates that the combination of stabilizers is completely unsuitable for this application.

Example 9

Propylene-ethylene copolymer containing 1,8% ethylene with a flow index of 4 dg / min, containing stabilizers Θ, 08% A1, 0,1 *% A3, 0,02% P1 0,02% P3 and 0,08% CaST was treated in the same manner as in Example 1.

Table 2 shows the results of the laboratory tests.

In terms of processing stability and the presence of gray granules, the formulation appears to be good, although it shows a somewhat reduced degree of whiteness.

Example i 0

Propylene e ethylene copolymer containing 16% ethylene with a flow index of 6 dg / min stabilizers 0.1% Al, 0.04% P2 0.04% P5 and 0.08% CaST was treated in the same manner as in Example 1. Laboratory test results see Table 2; In terms of processing stability and the occurrence of gray granules, the formulation appears to be good, although it shows a somewhat reduced degree of whiteness.

Claims (1)

PATENTOVÉ Claims Polypropylene and propylene copolymers with 0.1 to 20% by weight of ethylene containing 0.01 to 1% by weight of phenolic stabilizers and 0.01 to 1% by weight of a mixture of phosphate stabilizers, based on the polymer matrix and optionally further processing additives, characterized in that the mixture The phosphite stabilizers consist of 10 to 90% by weight of non-hydrolysable phosphites and 10 to 90% by weight of easily hydrolyzable phosphites.